In a typical polishing machine, there are usually two opposing plates, an upper plate and a lower plate. These plates are typically ring-shaped having an inner circumference and an outer circumference. A central rotary gear, sometimes referred to as a "sun" gear, is positioned within the inner circumference of the plates and a fixed external gear, sometimes referred to as a "ring" gear, is positioned about the outer circumference of the plates. Polishing pads are secured to the upper and lower plates to polish workpieces such as nickel plated aluminum disks. The polishing pads comprise a soft felt-like material such as that manufactured by Rodel as product Politex DG. Workpiece carriers having a plurality of teeth about their peripheries mesh on the fixed external gear and on the central rotary gear and are thereby rotated between the plates so that each of the workpieces contained in the carriers are subject to a cyclical movement independent of the movement of the polishing plates. The combined cyclical movements of the carriers and the plates effects a maximum uniform machining of the workpieces with the aid of an abrasive which can be placed between the plates. The abrasive may be suspended in a fluid to form a slurry, such as an aluminum oxide slurry, which functions in polishing the workpiece by entering through holes in the upper plate.
The polishing machines, which contain pins or gears for turning the workpiece carriers, must undergo frequent maintenance to ensure their mechanical structure is continuous in order to continue to provide for the uniform machining of workpieces. During processing of the workpieces, the nickel/slurry build-up created from the polishing action slurry flow can build up on the polishing surface and spill over into the pin or gear assemblies which drive the rotation of the workpiece carriers.
Typical grinding machines comprise much of the same structure as the polishing machine, such as opposing upper and lower grinding plates, a central rotary gear, and a fixed external gear. However, the upper and lower grinding plates are much thinner and instead of a polishing pad, grinding machines use segmented stone pieces which are attached to aluminum mounting plates that are secured to the upper and lower grinding plates in order to process the workpieces.
Abrasive foam grinding structures generally known as "honing stones", and more particularly known as "polyvinyl alcohol (PVA) stones" are used in grinding machines to grind or hone the surface of a workpiece. PVA stones typically have open cell structures or closed cell structures. Stones having an open cell structure are generally made from a combination of polyvinyl alcohol (PVA), starch, and a silicon carbide filler functioning as the abrasive material. An appropriate catalyst, for example sulfuric acid and/or formaldehyde, is then added to the PVA, starch and silicon carbide mixture to convert the mixture to a rubber-like mass with starch particles randomly entrained therein. The starch may then be flushed out from the composite with hot water and the remaining material may be impregnated with a stiffening agent.
When used to hone or grind workpieces, open-cell stones typically flake, liberating particulates at the stone-workpiece interface. Accordingly, the workpieces are typically flushed with water or a water-based solution during processing to remove the stone particulates and particulates liberated from the workpiece and to cool the interface which is heated by the grinding process.
Prior art references do exist which address some of the problems associated with polishing and grinding machines such as the heat created at the polishing or grinding interface and the slurry build-up at that same interface between the stone or pad and the workpiece. For example, U.S. Pat. No. 4,481,741 issued to Bouladon et al. describes a polishing machine having a rotating plate that is heat conditioned with the aide of nozzles disposed in the bottom of a tank for spraying a liquid against the lower face of the plate. In the Bouladon et al. apparatus, the plate is disposed inside of the tank and the nozzle is located in the bottom of the tank so that it can spray a liquid against the lower base of the plate. Further, U.S. Pat. No. 5,113,622 issued to Nishiguchi et al. describes an apparatus for grinding a semi-conductor workpiece which has a rotatable work stage. The apparatus has an inlet flow path for guiding cooling liquid to a grinding surface of the grinding wheel in order to perform cooling and an outlet flow path for collecting the cooling liquid which flows onto the work stage. The apparatus is also capable of detecting a temperature of the recovered cooling liquid by a temperature detector which is disposed in the outlet flow path. The rotational speed of the grinding wheel or the rotary table is then controlled based upon the temperature of the cooling liquid that is measured in the outlet flow path.
U.S. Pat. No. 4,991,358 issued to Giebmans describes a grinding machine with a grinding wheel which has a cooling medium storage tank that conducts a cooling medium via a nozzle to a contact region between the grinding wheel and a workpiece mounted on the workpiece table. As indicated in the previously described prior art references, this prior art reference addresses the problem of cooling the interface between the workpiece and the grinding stone in order to decrease the heat created as a result of the friction between the workpiece and the grinding stone.
Further, U.S. Pat. No. 4,216,630 issued to Smart et al. discloses a grinder apparatus with a pollution control fluid dispensing means. More particularly, this patent reference discloses nozzles which atomize water particles that are then directed toward a workpiece upon which a grinding operation is being performed. The nozzles are located adjacent the grinding tool and are aimed at the region of the grinding tool at which the particulate contaminants are generated in order to capture respirable micron and sub-micron sized particulate contaminates generated by the grinding operation. This patent reference is specifically directed toward removing respirable contaminants which are generated as a result of the grinding.
The prior art addresses the use of flushing the workpieces with a coolant to cool the grinding stone/workpiece interface and remove particulates from that interface. However, the nickel/slurry build-up in the pin or gear teeth assemblies can cause the uneven wearing of the gear teeth on the workpiece carriers which can ultimately result in a nonuniform machining of a workpiece. Further, slurry build-up will result in increased wear and tear on the pins or gears of the machines and the potential failure and/or shut down of the machines, especially the polishing machines. Accordingly, there is a need for a method and apparatus for removing the nickel/slurry build-up during polishing, and any other particulate build-up during grinding, from the pin or gear teeth assemblies which drive the rotation of the workpiece carriers.